THE FLYING EARTH 117 



Archimedes, and deposited by Marcellus in the temple of virtue 

 at Rome, was a very ancient invention, and that the first had 

 been made originally by Thales of Miletus ; but that the motion 

 of the sun and the moon and the five planets, or wandering stars, 

 could not be represented by this primitive solid globe ; and 

 that in this the invention of Archimedes was admirable, because 

 he had calculated how a single revolution should maintain un- 

 equal and diversified progressions (of the planets) in dissimilar 

 motions. In fact, when Gallus moved this globe, we observed 

 that the moon succeeded the sun by as many turns of the wheel 

 in the machine as days in the heavens. From whence it resulted 

 that the progress of the sun was marked in the heavens, and that 

 the moon touched the point where she is obscured by the 

 earth's shadow at the instant the sun is at the opposite side." 



The remainder of the passage is lost. But as any one who 

 has ever inspected an orrery must know, the construction of 

 this highly complex mechanism required not merely an extra- 

 ordinary ingenuity, but all that mathematics might teach as 

 well. We know, moreover, from many a passage in the works 

 of Cicero and elsewhere, that it was the demonstrations of 

 Archimedes, rather than of Aristarchus, which spread among 

 the enlightened people of that day the doctrine of the vast size 

 of the sun, the littleness of the earth. 



We know, too, that even in Archimedes' day, some reflective 

 minds had already begun to picture certain of the planets as 

 having the sun at the centre of their orbits, rather than the 

 earth. Long and thoughtfully had they watched the course 

 of the " wanderers," had seen them rise and set like the sun and 

 the moon, wax and wane in brilliancy ; observed Venus when 

 it casts a shadow, and again when it has shrunk to the size 

 of Saturn ; seen Mars blaze out in redness, then shrink away 

 to hardly more than a point. That Venus and Mars, Saturn 

 and Jupiter were of the same general nature as the moon, had 

 long been known. It was clear enough that the moon revolved 

 about the earth and not about the sun. This naturally led to 

 the idea that all planets did the same ; but it was disturbing 

 to see Venus now crossing the face of the sun, now obscured 

 by it. And so perchance with Mercury. 



Perhaps the sun, like the earth, might have its satellites, 

 and it was thus, apparently, that Mercury and Venus were 



